Research on Hepatitis C (HC) has followed several lines. Following cloning and sequencing the genome of the H strain of HCV, we have constructed a putative full length cDNA clone of the genome. We have been evaluating tha clone in cell culture systems as well as by direct transfection of RNA transcripts of this clone into chimpanzee liver. To date this clone has no proved to be infectious and we are in the process of modifying it with the hopes of having an infectious clone. Using recombinant baculovirus expresse protein we are developing an anti-HCV core specific for IgM. We hope to us such an assay to distinguish between patients who have recovered from patients who are asymptomatic but chronically infected. Such an assay may also prove useful in following patients on treatment protocols. In collaboration with C. Rice we have characterized the NS3 protease, identified the enzymatic active site, determined the processing of the entire HCV polyprotein and determined the precise cleavage sites of the NS3 protease. We have shown that all the cleavages downstream of the NS3 are performed by that protease, that all the cleavages in the structural protei region are performed by host peptidase probably signalase. However the cleavage between NS2 and NS3 was not performed by either signalase or the NS3 protease. Viral proteases may serve as targets for antiviral drugs and since the NS3 is a rather typical trypsin-like serine protease, inhibitors may not be viral specific. The NS2 protease however seems to be unique and therefore may be sensitive to specific inhibitors. We also have very preliminary evidence for further processing of the core protein that may be an autocatalytic event similar to what has been found in pestiviruses. We have a recombinant vaccinia virus containing the entire open reading frame of the HCV genome which we will evaluate in the chimpanzee model as a potential vaccine.